Systems and methods for facet joint treatment

ABSTRACT

A method of treating a facet joint of a patient. The facet joint includes a superior articular face and an inferior articular face. An implant is secured to an implant insertion tool by mating a first engagement feature on the implant with a second engagement feature on the implant insertion tool. A distal end of a guide cannula is positioned proximate the facet joint. The guide cannula has an internal passage extending therethrough. The implant slides through the guide cannula passage until the implant passes through a distal end of the guide cannula passage and is at least partially between the superior articular face and the inferior articular face. A force of at least 1 Newton is exerted on the implant insertion tool to separate the first engagement feature and the second engagement feature.

REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.13/084,104, which was filed on Apr. 11, 2011, and this applicationclaims priority to U.S. Provisional Application No. 61/355,140, whichwas filed on Jun. 15, 2010, the contents of which are incorporatedherein by reference.

FIELD OF THE INVENTION

An embodiment of the invention relates to a system for treating facetjoint pain. More particularly, the invention relates to an implantsystem for treating facet joint pain.

BACKGROUND OF THE INVENTION

Within the next ten years, more than seventy million people will jointhe ranks of seniors. In an aging population, the articular cartilagethat allows bones to smoothly move over each other wears down with timeand disease, and like many tissues in the body, articular cartilage hasa limited ability to heal itself.

At this time, options that help to relieve severe degenerative jointpain, or osteoarthritis, include joint replacement or fusion. Asexamples, approximately 200,000 total knee joint replacement operationsand over 300,000 hip joint replacement operations are performedannually. While these operations are generally effective at treating theaffected joint, these artificial joint implants typically only lastabout 10-15 years.

Chronic lower back pain also affects both work force productivity andhealthcare expense. There are currently over 500,000 surgical proceduresperformed annually in the United States in an attempt to alleviate lowerback pain even though such surgical procedures are typically onlyperformed after the failure of more conservative therapy such as bedrest, pain and muscle relaxant medication, physical therapy or steroidinjection. The source of this pain may originate from dysfunction amonga plurality of anatomical structures (as described below) that arecomprised in the spine, including facet joints.

To understand spinal biomechanics, and the impacts of dysfunction intherapy, it is useful to first consider the spinal anatomy. Thevertebrae of the spine are conventionally subdivided into severalsections. Moving from the head (cephalad) to the tailbone (caudal), thesections are cervical, thoracic, lumbar, sacral, and coccygeal.

Regardless of location, each vertebra forms two pedicles and two laminaethat combine to define a spinal foramen in which the spinal cord isprotected. Extending laterally from the pedicles are two transverseprocesses. Extending from the mid-line of the vertebra where the twolaminae meet is a spinous process. These three processes serve as aconnection point for ligaments and muscles.

Adjacent vertebrae are separated by an intervertebral disc and surfacesof the adjacent vertebrae form portions of two facet joints by andbetween the two vertebrae. Relative to a spinal segment consisting of anintermediate vertebra, an immediately adjacent cephalad vertebra, and animmediately adjacent caudal vertebra, the intermediate vertebra formsportions of four facet joints; namely, two facet joints with thecephalad vertebra, and two facet joints with the caudal vertebra.

With the above background in mind, FIGS. 1A and 1B illustrate a facetjoint 20 composed of a superior articular facet 22 and an inferiorarticular facet 24. The superior articular facet 22 is formed by thevertebral level below the intervertebral disc (i.e., a superiorarticular facet projects upward from the junction of the lamina and thepedicle), whereas the inferior articular facet 24 is formed by thevertebral level above the intervertebral disc (i.e., an inferiorarticular facet projects downward).

On the superior articular facet 22 is a superior articular face 26, andon the inferior articular facet 24 is an inferior articular face 28.Facet joints are oriented obliquely to the sagittal plane, and the jointspace itself is curved from front to back. The more posteriorly locatedinferior face 28 is convex, whereas the more interiorly located superiorface 26 is concave.

The facet joint 20 is a synovial joint that is defined by the twoopposing bony faces 26, 28 with cartilage 30 between them and a capsule32 around the joint 20. More specifically, synovial fluid 34 iscontained inside the joint 20 by the capsule 32, that is otherwise awater-tight sac of soft tissue and ligaments that fully surrounds andencloses the joint 20, and keeps the joint faces 26, 28 lubricated.

The ends of the bone articular facets 22, 24 that make up the synovialfacet joint 20 are normally covered with the articular, hyalinecartilage 30 that allows the bony faces 26, 28 to glide against oneanother, providing the flexibility that allows the movement of vertebralbodies relative to one another.

As indicated above, there are two facet joints between each pair ofvertebrae, one on each side (located posterior and lateral of thevertebral centerline), from the top and bottom of each vertebra. Thejoints combine with the disc space to create a three joint complex ateach vertebral level, and each joint extends and overlaps neighboringvertebral facet joints, linking each other and hence the vertebratogether.

The assembly of two vertebral bodies, the interposed spinal disc and theattached ligaments, muscles, and facet joints (inferior articulatingprocesses that articulate with the superior articular processes of thenext succeeding vertebra in the caudal direction) is referred to as a“spinal motion segment.” Each motion segment contributes to the overallflexibility of the spine and contributes to the overall ability of thespine to provide support for the movement of the trunk and head, and inparticular, the facet joints limit torsional (twisting) motion.

When the facets of one or more vertebral bodies degenerate or otherwisebecome damaged such that the vertebrae no longer articulate or properlyalign with each other, there is a resulting loss of mobility and pain ordiscomfort. The functional role of the facet joints in a spinal motionsegment is thus relevant to an understanding of the operative andfunctional advantages of the facet joint systems and methods disclosedherein, which achieve dynamic stabilization and mobility preservationwithout constraining motion in any plane.

As indicated above, facet joints are located on the posterior column ofthe spine. The context of this discussion: “anterior” refers to in frontof the spinal column, and “posterior” refers to behind the column;“cephalad” means towards a patient's head (sometimes referred to as“superior”); and “caudal” (sometimes referred to as “inferior”) refersto the direction or location that is closer to the patient's feet.

Facet joints can be arthritic due to degeneration with aging, trauma, ordisease (e.g., pathologies that include inflammatory, metabolic, orsynovial, disorders). In addition, fractures, torn ligaments, and discproblems (e.g., dehydration or herniation) can all cause abnormalmovement and alignment, putting extra stress on the surfaces of thefacet joint.

The physiological response to this extra pressure is the development ofosteophites, i.e., bone spurs. As the spurs form around the edges of thefacet joint, the joint becomes enlarged, a condition called hypertrophy,and eventually the joint surfaces become arthritic. When the articularcartilage degenerates or wears away, the bone underneath is uncoveredand rubs against bone. The joint thus becomes inflamed, swollen, andpainful.

Facet joint arthritis is a significant source of neck and back pain, andis attributable to about 15-30% of persistent lower back paincomplaints. Upon failure of conservative treatment for facet joint painsuch as intra-articular steroids/local anesthetic injectionsadministered under fluoroscopic guidance, some patients with chronicpain may eventually require surgical intervention for facet jointarthritis including, for example, facet rhizotomy; facet ectomony toremove the facet joint to reduce pressure on the exiting nerve root;total joint replacement or facet arthrodesis (i.e., fixation leading tofusion, where the two articulating surfaces of the joint remain immobileor grow solidly together and form a single, solid piece of bone); etc.

While these surgical procedures may alleviate back pain, many jointreplacements and all fusions do not restore the normal physiologicalfunction and motion attributable to healthy anatomical form. Rather,they often significantly alter spinal biomechanics that can in turncause or exacerbate co-existing spinal instabilities and degeneration atother spinal levels or in other joints associated with spinal motion.

There is a cause-and-effect relationship among intervertebral discintegrity, facet loads, and spinal degeneration. Specifically, theprogressive loss of disc height with disc degeneration often also altersthe facet joint's mechanical ability as the facet joints degenerate ordislocate, and ligaments lose elasticity and their load-carryingability. More specifically, with disc-space narrowing, as frequentlyoccurs with degenerative disc disease, there is an increased load in thefacet joints, especially in extension, and concomitant degeneration ofthe facet joints and capsules.

Since the facet joint capsules are primarily loaded in flexion and inrotation, and the facet joints are the primary resistors againstrotational or torsional forces (e.g., normally, the facet joints controlapproximately 30% of axial rotation), facet joint degenerationsignificantly alters spinal mobility.

The need to provide minimally invasive therapies that provide painrelief while restoring and preserving the biomechanical function of thephysiological facet joints is paramount to overall spinal mobility, andto date, therapies have not adequately satisfied all of these issues, asnoted below.

One therapy, facet rhizotomy, involves techniques that sever smallnerves that go to the facet joint. The intent of the procedure is tostop the transmission of pain impulses along these nerves. The nerve(s)is identified using a diagnostic injection. Then, the surgeon inserts alarge, hollow needle through the tissues in the low back. Aradiofrequency probe is inserted through the needle, and a fluoroscopeis used to guide the probe toward the nerve. The probe is slowly heateduntil the nerve is severed.

Another technique using pulsed radiofrequency does not actually burn thenerve, rather it is believed to stun the nerve. Yet another techniqueinvolves denervation by probe tip freezing, and still another procedureinvolves carefully controlled injection of botox toxin to treat musclespasm, a protective reflex that may occur when the facets are inflamedthat in turn causes the nearby muscles that parallel the spine to gointo spasm.

While these procedures may provide pain relief, they do not addressongoing joint degeneration (e.g., wear on articulating surfaces), whichleads to kinematic and biomechanical dysfunction that may in turn leadto transition syndrome (i.e., progression of degeneration and pain toother joints) at other levels.

While certain clinicians have advocated prosthetic total jointreplacement of damaged facet joints, in practice, it is difficult toimplement such a prosthesis for a variety of reasons including thevariability of facet joint geometry from facet joint to facet joint, andthe high level of interaction between the facet joint and the othercomponents in the spinal column.

Moreover, joint replacement is a highly invasive and time-consumingprocedure, requiring pre-preparation of joint surfaces and removal ofbone, and thus there are associated risks, including blood loss andmorbidity, increased anesthesia time, and increased convalescence time.

A related therapeutic treatment of the facet joint entails the provisionof an artificial facet joint where the inferior facet segment, themating superior facet segment, or both, are covered with a cap (i.e.,over all, or substantially all, of the facet). One such device andrelated method of implantation is described in Fitz, U.S. Pat. No. Re36,758.

While potentially viable, the capping of the facet segments has severalpotential disadvantages. Clinical concerns are believed to result fromthe disruption of the periosteum and ligamenturn teres femoris, bothserving a nutrition delivery role to the femoral head, thereby leadingto avascular necrosis of the bony support structure for the cap.

Another potential disadvantage of facet capping is that to accommodatethe wide variability in anatomical morphology of the facets, not onlybetween individuals, but also between levels within the spinal column, avery wide range of cap sizes and shapes is required.

Even further, implantation of the caps, such as those described in U.S.Pat. No. Re 36,758, cannot be performed on a minimally-invasive basis,and entail fairly significant preparatory steps at the implantation site(e.g., removal and/or re-shaping of bone). At least with use of capsover osteoarthritic femoral heads, the capping of articular bone endshas sometimes experienced clinical failure by mechanical loosening.

Another therapeutic treatment of the facet joint is to affix thesuperior articular process to the inferior articular process using afacet screw. Although the fixation therapy may alleviate symptomsassociated with a degenerated facet joint, it also sacrifices some ofthe ability of the motion segment to move and thus sacrifices some ofthe ability of the spinal column to move in a natural manner.

Central and lateral spinal stenosis (joint narrowing), degenerativespondylolisthesis, and degenerative scoliosis may all result from theabnormal mechanical relationship between the anterior and posteriorcolumn structures and induce debilitating pain.

More recently, a percutaneously-implantable, facet joint stabilizationdevice has been developed, and is described in U.S. application Ser. No.12/238,196 (filed Sep. 25, 2008 and entitled “Method and Apparatus forFacet Joint Stabilization”), the teaching of which are incorporatedherein by reference. The facet joint stabilization device generallyentails a superior body and an inferior body that, when combined, forman exteriorly threaded device.

When inserted into the joint space, the inferior and superior bodiesestablish an engaged relationship with the corresponding inferior andsuperior bony faces of the facet joint anatomy, respectively, and aresomewhat slidable relative to one another to facilitate near normalfacet joint motion ability. While viable, areas for improvement remain,including retention, long-term functioning, and insertion techniques.

As the present disclosure contemplates accessing various vertebralelements and joints through a preferred approach that comes in from apercutaneous posterior approach, “proximal” and “distal” are defined incontext of this channel of approach. Consequently, “proximal” is closerto the beginning of the channel and thus closer to the clinician, and“distal” is further from the beginning of the channel and thus moredistant from the clinician.

When referencing access or delivery tools, “distal” would be the endintended for insertion into the access channel, and “proximal” refers tothe opposing end, generally the end closer to the handle of the deliverytool. When referencing implants, generally “distal” would be the leadingend first inserted into the joint and “proximal” refers to the trailingend, generally in an engagement with a deployment tool.

In light of the above, a need exists for additional therapies applicableto facet joints to stabilize and augment the facet joint in alleviatingproblems without initial resort to the more radical therapies ofreplacing the facet joint with a prosthesis and/or fixation of the facetjoint and the inherent loss of natural movement of that motion segment.

SUMMARY OF THE INVENTION

Some aspects in accordance with the invention relate to a system fortreating a facet joint of a patient. The facet joint anatomy includesopposing, superior and inferior articular faces. With this in mind, thesystem includes a superior resurfacing device and an inferiorresurfacing device.

The superior resurfacing device has a superior resurfacing bodyconfigured to selectively transition to a shape conforming to a shape ofthe superior articular face of the facet joint. Similarly, the inferiorresurfacing device includes an inferior resurfacing body configured toselectively transition to a shape conforming to a shape of the inferiorarticular face of the facet joint.

In this regard, each of the resurfacing bodies exhibits sufficientflexibility to transition from a relatively flat state to an insertedstate in which the resurfacing body substantially matches anymulti-planar curvatures and concavities of the corresponding facet jointarticular face in the presence of compressive forces associated with atypical, adult human facet joint.

With this construction, the system is capable of establishing a newsliding interface within the facet joint via articulating surfaces ofthe resurfacing bodies, thereby eliminating the pain-causing,bone-on-bone articular interface associated with the natural anatomy.Further, by conforming to the natural shape associated with the nativefacet joint articular faces, the system of the invention can be insertedon a minimally-invasive basis, and restructuring (e.g., removal) of thenatural bony interface is not required.

In some embodiments, the resurfacing bodies are identical, eachconsisting of a disc-like body having a thickness in the range ofbetween about 0.25 and about 4 millimeters. In related embodiments, theresurfacing bodies are formed of polyetherketone (PEK)-based material,such as polyetheretherketone (PEEK).

In yet other embodiments, the resurfacing bodies provide an articulatingsurface and a plurality of teeth projecting in a direction opposite thearticulating surface; the plurality of teeth serve to establishengagement with the corresponding facet joint articular face uponinsertion.

Yet other aspects in accordance with principles of the invention relateto methods for treating facet joint pain of a patient, and includeinserting a superior resurfacing body into the facet joint and intoengagement with the superior articular face of the facet joint articularanatomy. In this regard, the superior resurfacing body transitions froma relatively flat state to an insertion state upon insertion to thefacet joint, substantially conforming to a shape of the superior facetjoint face in response to compressive forces of the facet joint.

An inferior resurfacing body is inserted into the facet joint and intoengagement with an inferior facet joint articular face. As part of thisinsertion, the inferior resurfacing body transitions from a relativelyflat state to an insertion state that substantially conforms to a shapeof the inferior articular face in response to compressive forces of thefacet joint.

Upon final insertion, an articulating surface of the superiorresurfacing body slidably abuts an articulating surface of the inferiorresurfacing body, thereby relieving facet joint pain. In someembodiments, the method is characterized by the absence of surgicalremoval of normal bone of the facet joint, and the resurfacing bodiesare inserted simultaneously via a percutaneous technique.

Yet other aspects in accordance with principles of the presentdisclosure relate to a kit for treating a facet joint of a patient. Thekit includes a treatment system as described above (e.g., a superiorresurfacing device having a superior resurfacing body, and an inferiorresurfacing device having an inferior resurfacing body), along with aninsertion tooling set. The insertion tooling set may include a deliverycannula and an implant insertion tool.

The delivery cannula has a distal end and defines an internal passagethat is open at the distal end. The implant insertion tool is sized tobe slidably received within the passage. With this construction, the kitis configured to provide an insertion arrangement in which theresurfacing devices and the implant insertion tool are slidably receivedwithin the passage, with the resurfacing devices being stacked againstone another adjacent the distal end and a distal region of the implantinsertion tool abutting the resurfacing devices opposite the distal endof the cannula. In some embodiments, the resurfacing devices each have arecess to receive a finger formed by the implant insertion tool toachieve selective engagement therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIG. 1A is a simplified cross-sectional view of a human spinal segmentillustrating anatomy of native facet joints with which the systems andmethods of the present disclosure are useful in treating.

FIG. 1B is an enlarged view of one facet joint of the segment of FIG.1A.

FIG. 2 is a perspective view of a resurfacing body according to anembodiment of the invention.

FIG. 3 is a side view of the resurfacing body of FIG. 2.

FIG. 4 is top view of another configuration of the resurfacing bodyhaving a tab extending therefrom.

FIG. 5 is a sectional view of the resurfacing body taken along a lineA-A in FIG. 4.

FIG. 6 is a perspective view of the resurfacing body of FIG. 4.

FIG. 7 is a top view of another configuration of the resurfacing bodyhaving a tab extending therefrom.

FIG. 8 is a sectional view of the resurfacing body taken along a lineA-A in FIG. 7.

FIG. 9 is a perspective view of the resurfacing body of FIG. 7.

FIG. 10 is a top view of a guide probe assembly according to anembodiment of the invention.

FIG. 11 is a sectional view of the guide probe assembly taken along aline A-A in FIG. 10.

FIG. 12 is an enlarged sectional view of a tip portion of the guideprobe assembly.

FIG. 13 is a side view of a guide probe assembly according to analternative embodiment of the invention.

FIG. 14 is a perspective view of a guide cannula for use in conjunctionwith an embodiment of the invention.

FIG. 15 is a side view of the guide cannula of FIG. 14.

FIG. 16 is a side view of a delivery cannula according to an embodimentof the invention.

FIG. 17 is a side view of an implant insertion tool according to anembodiment of the invention.

FIG. 18 is a side view of an implant insertion tool according to analternative embodiment of the invention.

FIG. 19 is a side view of an implant insertion tool according to anotheralternative embodiment of the invention.

FIG. 20 is a side view of an implant countersink positioner according toan embodiment of the invention.

FIG. 21 is a top view of the resurfacing device positioned adjacent to adistal end of the implant insertion tool.

FIG. 22 is a perspective view of the resurfacing device in engagementwith an extension on the distal end of the implant insertion tool.

FIG. 23 is a perspective view of the delivery cannula inserted into theguide cannula.

FIG. 24 is a perspective view of the implant insertion tool in aninitial position where the resurfacing device is inside of the deliverycannula and where the delivery cannula is inside of the guide cannula.

FIG. 25 is a perspective view of the implant insertion tool in aninserted position where the resurfacing device is partially extendingbeyond the distal end of the delivery cannula.

FIG. 26 is a perspective view of the implant insertion tool in apartially retracted position where the resurfacing device is movedbeyond the delivery cannula for implanting the resurfacing device in thefacet joint.

FIG. 27 is a side view of a leaflet retractor tool for use inwithdrawing the implant insertion tool from the delivery cannula.

FIG. 28 is a perspective view of the guide probe assembly inserted intothe facet joint and the guide cannula being inserted over the guideprobe assembly.

FIG. 29 is a sectional view of the resurfacing device that has beenimplanted in one of the facet joints.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of an implant system 40 in accordance with principles ofthe invention and useful for treating a facet joint of a patient isillustrated in FIG. 2. The implant system 40 may include a superiorresurfacing device 42 and an inferior resurfacing device 44.

As illustrated in FIG. 2, the superior resurfacing device 42 may bepositioned on top of the inferior resurfacing device 44 so that thesuperior resurfacing device 42 and the interior resurfacing device 44are oriented in opposite directions as the superior resurfacing device42 and the inferior resurfacing device 44 would be oriented during theimplantation process. Details on the various components of theresurfacing devices 42, 44 are provided below.

In certain embodiments, the resurfacing devices 42, 44 may besubstantially similar to each other where the superior resurfacingdevice 42 is placed adjacent to a superior facet joint articular face(e.g., the superior articular face 26 of FIG. 1B), and the inferiorresurfacing device 44 is placed adjacent to an inferior facet jointarticular face (e.g., the inferior articular face 28 of FIG. 1B).

The resurfacing devices 42, 44 may be capable of substantiallyconforming to the naturally-occurring shape or curvature of the facetjoint anatomy. The resurfacing devices 42, 44 thereby replace thebone-on-bone interface of the natural facet joint in a manner achievingnormal or near normal mobility.

While not required, the resurfacing devices 42, 44 may be substantiallysimilar to each other in some embodiments. As such, the followingdescription of the superior resurfacing device 42 is equally applicableto the inferior resurfacing device 44.

The resurfacing device 42 consists of a resurfacing body 46. In certainembodiments described below, one or more additional components can beattached to, or extend from, the resurfacing body 46. In certainembodiments, the resurfacing body 46 may have a disc-like shape, thatincludes a base web 50 and a plurality of teeth 52 (referencedgenerally).

The base web 50 defines opposing major surfaces 54, 56, as illustratedin FIG. 3, with the first major surface 54 providing or serving as anarticulating surface (e.g., articulates relative to a correspondingarticulating surface of the inferior resurfacing device 44 (FIG. 2)) asdescribed below. Thus, the first major surface 54 may also be referencedas the “articulating surface” of the resurfacing body 46. The pluralityof teeth 52 may project from the second major surface 56 in a directionthat is generally opposite the first major surface 54.

With specific reference to FIGS. 2 and 3, the base web 50 defines anouter perimeter 58 of the resurfacing body 46. In certain embodiments,the outer perimeter 58 may have a generally circular shape thatgenerally conforms to a shape of the facet joint in which theresurfacing body is to be implanted. In other embodiments, the perimetermay have an oval-like shape (relative to a top or bottom plan view). Theresurfacing device 44 may be formed with other shapes, examples of whichinclude square, rectangular, hexagonal and curvilinear.

An overall size or footprint of the resurfacing body 46 is defined bythe outer perimeter 58 and can vary depending upon a size of the facetjoint being treated, but is generally relatively small, especially ascompared to conventional facet joint prostheses and/or capping devices.As is noted above, the resurfacing body 46 should be large enough toprevent bone-to-bone contact in the facet joint.

In certain embodiments, a diameter of the resurfacing body 46 may be inthe range of between about 3 millimeters and about 15 millimeters. Inother embodiments, the diameter of the resurfacing body may be in therange of between about 5 millimeters and about 10 millimeters.

Facet joint treatment systems in accordance with this invention may beprovided to a treating clinician with two or more different superiorresurfacing devices 42 (and two or more different inferior resurfacingdevices 44) each having a differently-sized resurfacing body 46.

Examples of the sizes of the resurfacing bodies include about 5millimeters, about 8 millimeters, about 10 millimeters and about 12millimeters. The treating clinician may select the most appropriatelysized resurfacing device for implantation based upon an evaluation ofthe facet joint to be treated.

While it is desirable for the resurfacing body 46 to be sufficientlylarge to prevent bone-to-bone contact within the facet joint, theresurfacing body 46 should not be too large such that the resurfacingbody 46 extends beyond the facet joint as such a condition could resultin damage to the tissue adjacent to the facet joint where theresurfacing body 46 is implanted.

For reasons that are set forth in more detail below, the resurfacingbody 46 may incorporate one or more features dictating a preferredinsertion orientation and/or direction. For example, the resurfacingbody 46 may be more readily inserted into, and subsequently retainedwithin, a facet joint in a particular orientation.

Relative to the configuration of FIGS. 2 and 3, the outer perimeter 58can be described as generally defining a leading or distal end 70, atrailing or proximal end 72, and opposing sides 74, 76. During aninsertion procedure, the resurfacing body 46 may be oriented such thatthe leading end 70 is initially inserted into the facet joint, followedby the trailing end 72.

In addition to the teeth 52 having a structure corresponding with thesedesignations (and thus the intended insertion direction and orientationdescribed below), the trailing end 72 can form or define an engagementfeature 80, as illustrated in FIG. 2, that promotes desired interactionwith a separately-provided insertion tool, which is discussed in moredetail below.

In certain embodiments, the engagement feature 80 is an aperture thatincludes at least two aperture regions 81 a, 81 b. The first apertureregion 81 a may intersect the outer perimeter 58 or edge proximate thetrailing end 72. The second aperture region 81 b is in communicationwith the first aperture region 81 a and is oriented on a side of thefirst aperture region 81 a that is opposite the outer perimeter 58.

The first aperture region 81 a may have a width that is smaller than awidth of the second aperture region 81 b. The shape of the engagementfeature 80 thereby provides a partially enclosed aperture to facilitateattachment of the resurfacing body 46 to the implant insertion toolduring the insertion process.

A force to separate the resurfacing body 46 from the implant insertiontool should be sufficiently large so that the resurfacing body 46 doesnot inadvertently separate from the implant insertion tool 312. Incertain embodiments, the force to separate the resurfacing body 46 fromthe implant insertion tool 312 is at least 1 Newton. In otherembodiments, the force to separate the resurfacing body 46 from theimplant insertion tool 312 is between about 1 Newton and about 10Newtons. In still other embodiments, the separation force is about 5Newtons.

The separation force may be affected by a difference in the sizes of thewidths of the first aperture region 81 a and the second aperture region81 b and the width of the extension. The separation force may also beaffected by other factors such as the rigidity of the resurfacing body46 and the extension on the implant insertion tool 312. For example, ifthe resurfacing body 46 or the extension is fabricated from a flexiblematerial, the separation force may be lower if the resurfacing body 46or the extension is fabricated from a relatively rigid material.

The engagement feature 80 may be formed at the same time the otherportions of the resurfacing body 46 are formed such as by molding.Alternatively, the engagement feature 80 may be formed after theresurfacing body 46 is formed such as by stamping out the region thatdefines the first aperture region 81 a and the second aperture region 81b.

It is possible to use other techniques for maintaining the resurfacingdevice 46 in engagement with the implant insertion tool 312 during theprocess of inserting the resurfacing device 46 into the facet joint. Anexample of one such alternative attachment technique is attaching theresurfacing device 46 and the implant insertion tool 312 with afrangible connection. When a force that is greater than a thresholdforce is applied, the frangible connection may be severed to therebyallow the implant insertion tool 312 to be removed while leaving theresurfacing body 46 in the facet joint. In certain embodiments, theforce to sever the frangible connection is at least 1 Newton. In otherembodiments, the force to sever the frangible connection is betweenabout 1 Newton and about 10 Newtons. In still other embodiments, theseparation force is about 5 Newtons.

In certain embodiments, the base web 50 has, in some constructions, arelatively uniform thickness (e.g., nominal thickness variation of+/−0.05 mm), as illustrated in FIG. 3. The base web 50 forms thearticulating surface 54 to be relatively smooth. This smoothnessattribute is, at least in part, a function of the material employed forthe resurfacing body 46 as described below.

In other embodiments, the articulating surface 54 of the base web 50 maybe coated with a separate layer that provides enhanced frictional (i.e.,lower coefficient of friction) and wear characteristics. An example ofone such material having a low coefficient of friction ispolytetrafluoroethylene (PTFE), which is available under the designationTEFLON.

The plurality of teeth 52 project from the second major surface 56 ofthe base web 50. These teeth 52 may have a variety of forms. In someembodiments, the teeth 52 are arranged to form or define discrete zonesor teeth sets, such as the first, second and third teeth sets 90, 92, 94generally identified in FIG. 2.

The first teeth set 90 may be centrally located along the base web 50extending between the leading and trailing ends 70, 72. Individual teethof the first teeth set 90 may be generally identical. More particularly,each of the teeth may include a leading face 98 and a trailing face 100that extends from the second major surface 56 and intersect at a tip102. The leading face 98 may be oriented more proximate the leading end70 (as compared to the trailing face 100), whereas the trailing face 100may be oriented more proximate the trailing end 72.

With these designations in mind, the teeth may be constructed to definean insertion direction whereby an angle formed by the leading face 98relative to the second major surface 56 is smaller than an angle formedby the trailing face 100 relative to the second major surface 56.

In these configurations, the leading face 98 may have a more gradualslope relative to the leading end 70 as compared to a slope of thetrailing face 100 relative to the trailing end 72 such that the tooth 96a more overtly engages a separate structure, such as the facet jointsuperior face (not shown) at and along the trailing face 100 as comparedto the leading face 98.

In some configurations, the angle defined by the leading face 98 may bein the range of 20°-60°, whereas the angle defined by the trailing face100 is approximately 90°. Suitable angles may be affected by a varietyof factors such as the material from which the resurfacing body 46 isfabricated. Regardless, and returning to FIG. 2, the remaining teeth ofthe first teeth set 90 may be aligned with one another in two or morerows as shown.

The second teeth set 92 and the third teeth set 94 may be formed at oralong the opposing sides 74, 76, respectively, as illustrated in FIG. 2.In this regard, while the individual teeth of the second and third sets92, 94 may have the non-symmetrical relationship described above withrespect to the tooth discussed above, an exterior face 104 associatedwith each tooth of the second and third teeth sets 92, 94 establish anangle of extension relative to the second major surface 56 thatapproaches 90°.

With this but one acceptable construction, the second and third teethsets 92, 94 overtly resist side-to-side displacement of the resurfacingbody 46 relative to a corresponding facet joint face followinginsertion. For example, the second teeth set 92 may resist leftwarddisplacement of the resurfacing body 46, whereas the third teeth set 94may resist rightward displacement.

In certain embodiments, each tooth of the plurality of teeth 52 may havean identical, or nearly identical, height (or extension from the secondmajor surface 56), as illustrated in FIG. 3. In other embodiments, theteeth of the first teeth set 90 may have an elevated height as comparedto teeth of the second and third teeth sets 92, 94, and combine todefine a tapering height of the resurfacing body 46 from the leading end70 to the trailing end 72.

Stated otherwise, and relative to the illustrated embodiment in whichthe first major surface 54 is planar, a height of the leading tooth 96 ais greater than a height of a trailing tooth 96 b. For example, the tips102 associated with the teeth of the first teeth set 90 combine todefine a hypothetical plane P. The plane P is, in some embodiments,non-perpendicular relative to a plane of the first major surface 54,combining with the first major surface 54 to define an included angle inthe range of between about 1° and about 5°.

In other embodiments, other angles are also contemplated where the teeth52 have substantially similar heights. In certain embodiments, thetallest tooth 96 a may be provided at the leading end 70 that ultimatelyis located opposite the point of insertion into the facet joint. As aresult, the leading tooth 96 a may establish a more rigid engagementwith the corresponding facet joint face to thereby overtly resistdisplacement upon final insertion.

The base web 50 and the teeth 52 combine to define an overall thicknessT of the resurfacing body 46. For example, a lateral distance betweenthe first major surface 54 and the tip 102 of the “tallest” tooth 96 a.As described in greater detail below, a desired conformabilitycharacteristic of the resurfacing body 46 is influenced by the overallthickness T and the base web thickness t, and thus the overall thicknessT is selected, along with other parameters, to effectuate the desireddegree of conformability.

In some constructions, the overall thickness T of the resurfacing body46 is between about 0.25 millimeters and about 4 millimeters, althoughother dimensions are also contemplated. As a point of reference, theoverall thickness T associated with the resurfacing body 46 selected bythe treating clinician for insertion into a particular facet joint mayvary as a function of other procedures associated with the insertion.

For example, where the resurfacing body 46 is inserted into a facetjoint without any overt tissue removal prior to insertion, the overallthickness T can be between about 0.5 millimeters and about 2.5millimeters. If the insertion procedure entails first removing cartilage(or other tissue) from the facet joint, a larger version of theresurfacing body 46 can be inserted, such that the overall thickness Tof the resurfacing body 46 is between about 0.5 millimeters and about 3millimeters.

The resurfacing devices 42, 44, and thus the corresponding resurfacingbodies 46, may be integrally formed of a robust material that achievesdesired conformability. The resurfacing body 46 in accordance with thisinvention maintains its structural integrity (i.e., little or no wear)without adhesive or cohesive damage when subjected to typicalarticulation of the facet joint with movement of the patient.

In some constructions, the resurfacing devices 42, 44 may be formed ofan implantable-grade plastic, although other materials such as metal arealso available. For example, the resurfacing devices 42, 44 may be madefrom the polyetherketone (PEK) family of plastics, which have strength,wear, flexibility, and biocompatibility properties appropriate forinsertion into, and long-term functioning within, the facet joint.

Polyetheretherketone (PEEK) has been found to provide not only theconformability attributes described below, but also long-term mechanicalstrength and resistance to wear. Additional materials may beincorporated, such as those exhibiting radio-opacity properties. Forexample, the resurfacing devices 42, 44 may be formed from aradio-opaque mineral (e.g., barium)-loaded PEK composition.

Visualization may also be provided via one or more radio-opaque markerbands (e.g., platinum marker band). The marker band(s) can be embeddedwithin the resurfacing device 42, 44. For example, a radio-opaque rodmay be inserted into a hole formed in the resurfacing device 42, 44, asillustrated in FIG. 5. Alternatively, the radio-opaque material may beinserted around a perimeter of the resurfacing device 42, 44.

The selected materials, shapes, and dimensions associated with theresurfacing body 46 of each of the resurfacing devices 42, 44 impart orcreate a conformability property to the resurfacing body 46 sufficientto allow the resurfacing body 46 to “match” the multi-planar concavityassociated with a native facet joint articular face anatomy.

With the resurfacing device 42, 44 embodiment of FIG. 2, the resurfacingbody 46 forms an entirety of the corresponding resurfacing device 42,44. In other embodiments described below, one or more additionalcomponents may be included with the resurfacing body 46, such that thefollowing explanation of conformability is specifically applicable tothe resurfacing body 46, but may also apply equally to the resurfacingdevices 42, 44 as a whole.

In general terms, “conformability” may be inversely proportional tobending stiffness of the resurfacing body 46 during insertion, and maybe increased as the resurfacing body 46 heats to body temperature and isallowed to creep. From a clinical perspective, “conformability” of theresurfacing body 46 entails the resurfacing body 46 conforming to aradius of curvature of the C-shaped or J-shaped portions of thearticular joint such as the concave-shaped superior articular face 26 ofFIG. 1B or the convex-shaped inferior articular face 28 of FIG. 1B.

As a point of reference, the minimum radius of curvature of the humanfacet joint in the transverse plane is on the order of 20 millimeters,with a lower bound (10th percentile) on the order of 7 millimeters. Theradius of curvature will vary with the vertebral level and the patient'sspecific anatomy and disease state. Preparation of the facet joint priorto insertion of the resurfacing devices 42, 44 may also change theradius of curvature.

A range of curvature radii of 7 millimeters to infinity (i.e., flatfacet anatomy) can be accommodated by the resurfacing devices 42, 44 ofthe present disclosure. There also may be curvature in the sagittalplane; the conformable nature of the resurfacing body 46 of the presentdisclosure is capable of substantially “matching” any sagittal planecurvature as well.

With the above understandings in mind, the conformability characteristicof the resurfacing body 46 is sufficient such that the resurfacing body46 readily transition from the relatively flat state illustrated in FIG.2 to an inserted state (not shown but reflected, for example, in FIG.30) in which the resurfacing body 46 substantially matches or mimics thenaturally-occurring shape (e.g., radius of curvature of curved portions)of the facet joint face to which the resurfacing body 46 is secured. Inthis regard, the facet joint 20 (FIG. 1B) is subject to, or experiences,various loads that effectuate compressive forces at the region ofinterface between the superior and inferior articular faces 26, 28 (FIG.1B).

These physiologic forces across the facet joint 20 will vary withactivity, posture, body loads, and muscle forces, and tend to be betweenabout 7% and about 14% of body load when standing. However, in theprone, slightly flexed position during surgery/implantation, these loadsmay be as little as zero. The intrinsic forces will be generated as theresurfacing device 42, 44 (and thus the corresponding resurfacing body46) are inserted and the capsule 32 (FIG. 1B) is tensioned. Compressionof the underlying cartilage and subchondral bone, slight flexion, orlaminar strains may result and would accommodate some thickness of thedevices 42, 44. However, separation/posterior translation of thesuperior facets would be required to accommodate a large portion of acollective thickness of the devices 42, 44.

Compressive loads normal to and across the articular faces 26, 28 willbe generated upon separation/posterior translation of the superiorfacets due to joint capsule tensioning. The conformable nature of theresurfacing body 46 is such that in the presence of these typicalcompressive forces, the resurfacing body 46 will transition from therelatively flat state to the inserted state in which the resurfacingbody 46 substantially matches the geometry of the facet joint surface towhich the resurfacing body 46 is secured.

For example, the resurfacing body 46 will flex to conform with amacroscopic shape/contour of the native articular face to which theresurfacing body 46 is applied, but may not conform to the microscopicvariations in the native articular face because of small deviations dueto cartilage defects, bony fissures, or small voids during preparationof the joint (typically between about 0.05 millimeters and about 0.5millimeters in width).

This process will occur as the compressive forces applied by the ends ofthe hypothetical concave region of one facet articular surface (e.g.,the superior articular surface 26) and the center of the correspondingconvex surface on the opposing articular facet (e.g., the inferiorarticular surface 28) generate a bending moment on the resurfacing body46 that produces strain to conform the resurfacing body 46 to the nativeanatomy.

As used through this specification, a resurfacing body that conforms tothe minimum radius of curvature of an adult human facet joint undernormal physiologic forces (e.g., between about 180 and about 450Newtons/millimeter per segment assuming a net 1 millimeter posteriorshear translation) without deviations from the articular surface towhich the resurfacing body is applied of greater than 1 millimeter isdefined as being “conformable” and “substantially matching” themulti-planar curvatures of a facet joint.

Alternatively, a resurfacing body sized for placement within an adulthuman facet joint and exhibiting a Conformability Factor (describedbelow) of not more than 100 Newtons is also defined as being“conformable” and “substantially matching” the multi-planar curvaturesof a facet joint in accordance with the present disclosure. In someembodiments, resurfacing bodies in accordance with the presentdisclosure exhibit a Conformability Factor of not more than 50 Newtons,and in other embodiments not more than 25 Newtons.

It has surprisingly been found that forming the resurfacing body 46 (andthus either of the resurfacing devices 42, 44 of the one embodiment ofFIG. 2) of PEEK and with the footprint size and thickness dimensionsdescribed above achieves the desired conformability characteristics,long-term resistance to wear, and facet joint stabilization followinginsertion.

Another embodiment of the resurfacing body 46 is illustrated in FIGS.4-6. The resurfacing body 46 may have a similar over shape and a similartooth pattern to the resurfacing body illustrated in FIGS. 2-3 except asnoted below.

The resurfacing body 46 may include a radio opaque marker 82 placedtherein. The radio opaque marker 82 may be utilized to monitor thelocation of the resurfacing body 46 is implanted in a non-invasivemanner as the radio opaque marker 82 may be viewed using many differenttypes of imaging conventionally used in the medical field.

The radio opaque marker 82 should be sufficiently large to facilitateviewing the radio opaque marker using conventional medical imagingtechniques. However, the radio opaque marker 82 should be sufficientlysmall such that the radio opaque marker 82 does not impede theflexibility of the resurfacing body 46 after implantation. Alternativelyor additionally, the radio opaque marker 82 may be fabricated from aflexible material that does not impede the ability of the resurfacingbody 46 to flex after implantation.

While it is possible to incorporate the radio opaque marker 82 duringthe process used to fabricate the resurfacing body 46, it is alsopossible to insert the radio opaque marker 82 into the resurfacing body46 after fabrication.

One such suitable technique for inserting the radio opaque marker 82into the resurfacing device includes forming an aperture in theresurfacing body 46. In certain embodiments, the aperture may be formedusing a drill.

In certain embodiments, the radio opaque marker 82 may be placed intothe resurfacing body 46 from a trailing end 72 thereof proximate acenter line of the resurfacing body 46. Using such a configurationprovides the resurfacing body 46 with symmetry to assist in evaluatingthe position of the resurfacing body 46 based upon medical imaging ofthe radio opaque marker 82.

The placement of the radio opaque marker 82 in the resurfacing body 46should be relatively accurate such that the radio opaque marker 82 doesnot extend through one of the surfaces of the resurfacing body 46. Suchan occurrence could lead to degradation of the resurfacing body 46 orcould cause damage to the tissue in the facet joint that is adjacent tothe resurfacing body 46.

To ensure that the radio opaque marker 82 does not extend through theupper surface of the resurfacing body 46, an additional material region84 may be provided in the region adjacent to the radio opaque marker 82,as illustrated in FIGS. 4 and 5. The radio opaque marker 82 may beplaced at an approximately equal distance between the upper and lowersurfaces of the resurfacing body in the additional material region 84.

An elongated tab 86 may extend from the trailing end 72 of theresurfacing body 46. The elongated tab 86 could be used in themanufacturing process and then be severed from the other portions of theresurfacing body 46 once manufacturing is completed. Alternatively, theelongated tab 86 may be used in conjunction with the insertion of theresurfacing body 46 into the facet joint as opposed to the implantationsystem described herein. In such instances, a line of weakening may beprovided where the elongated tab 84 intersects the resurfacing body 46.

Another embodiment of the resurfacing body 46 is illustrated in FIGS.7-9. The resurfacing body 46 may have a similar over shape and a similartooth pattern to the resurfacing body illustrated in FIGS. 2-3 except asnoted below.

The resurfacing body 46 may include a radio opaque marker 82 placedtherein. The radio opaque marker 82 may be utilized to monitor thelocation of the resurfacing body 46 is implanted in a non-invasivemanner as the radio opaque marker 82 may be viewed using many differenttypes of imaging conventionally used in the medical field. The featuresand placement of the radio opaque marker 82 are similar to the featuresand placement of the radio opaque marker 82 in the embodiment of theresurfacing body 46 illustrated in FIGS. 4-6

An elongated tab 86 may extend from the trailing end 72 of theresurfacing body 46. The structure and function of the elongated tab 86may be to the structure and function of the elongated tab 86 in theembodiment of the resurfacing body 46 illustrated in FIGS. 4-6.

The resurfacing body 46, and thus the system 40, may be delivered to,and inserted within, a facet joint in a variety of manners via variousinstrumentations sets or systems. Components of one useful insertiontooling set are discussed below.

One of the important aspects of accurately delivering the resurfacingbody 46 is to not only accurately locate the desired facet joint butalso to accurately position the resurfacing body delivery system withrespect to the facet joint to permit the resurfacing body 46 to beaccurately inserted into the facet joint.

In certain embodiments, a guide probe assembly 200, as illustrated inFIGS. 10-11, may be initially used to locate the region in the facetjoint where the resurfacing device 46 is to be inserted. The guide probeassembly 200 may include a guide probe shaft 202 and a guide probe tip204 that extends from a distal end of the guide probe shaft 202.

The guide probe shaft 202 may have a substantially rectangular profile,as illustrated in FIGS. 10 and 11. Forming the guide probe shaft 202with the substantially rectangular profile enables the guide cannula 260to slide over the guide probe assembly 200 after the guide probeassembly 200 is positioned with the guide probe tip 204 at leastpartially in the facet joint, as is discussed in more detail herein.This process reduces the time associated with implanting the resurfacingbody 46 when compared to an implantation system that does not utilizethis insertion process.

To minimize the size of the incision that is formed in the patient, theguide probe shaft 202 may be formed with a width and a height that isapproximately equal to a width and a height of the resurfacing body 46.

In certain embodiments, the guide probe shaft 202 has a width of betweenabout 5 millimeters and about 20 millimeters. In other embodiments, theguide probe shaft 202 has a width of about 12 millimeters.

In certain embodiments, the guide probe shaft 202 has a thickness ofbetween about 0.20 millimeters and about 10 millimeters. In otherembodiments, the guide probe shaft 202 has a thickness of about 2millimeters.

The guide probe shaft 202 is formed with a length that enables aproximal end of the guide probe shaft 202 to be positioned outside ofthe patient's body when the distal end of the guide probe shaft 202 isadjacent the facet joint. Such a configuration facilitates the surgeonor other person who is using the guide probe assembly 200 to accuratelyposition the guide probe assembly 200 with respect to the facet joint.

In certain embodiments, the guide probe shaft 202 has a length ofbetween about 10 centimeters and about 30 centimeters. In otherembodiments, the guide probe shaft 202 has a length of about 23centimeters.

The distal end of the guide probe shaft 202 may include a tapered region206, as illustrated in FIGS. 10-11, to provide a transition between theguide probe shaft 202 and the guide probe tip 204. The length of thetapered region 206 may depend on a variety of factors such as adifference in the width and the height of the guide probe shaft 202 andthe guide probe tip 204.

The guide probe shaft 202 may be fabricated from a relatively rigidmaterial to facilitate the use of the guide probe shaft 202 to locatethe facet joint using the guide probe tip 204. In certain embodiments,the guide probe shaft 202 may be fabricated from stainless steel. Inother embodiments, it is possible to fabricate the guide probe shaft 202from a non-metallic material such as plastic.

An important criterion is that the guide probe shaft 202 be fabricatedfrom a material that is biocompatible. If it is desired to reuse theguide probe shaft 202 for multiple surgical procedures, the guide probeshaft 202 should be capable of withstanding repeated sterilizationprocesses such as by using an autoclave.

The guide probe tip 204 is operably connected to the proximal end of theguide probe shaft 202. In certain embodiments, the guide probe shaft 202has an aperture 210 formed in the distal end thereof. This aperture 210is adapted to receive a portion of the guide probe tip 204.

The portion of the guide probe tip 204 that extends into the aperture210 may have a length that is greater than a length of the guide probetip 204 that extends beyond the proximal end of the guide probe shaft202 to enhance the ability of the guide probe tip 204 when attempting tolocate a desire location in the facet joint.

Forming the guide probe tip 204 separate from the other portions of theguide probe assembly 200 enables guide probe tips 202 having differentwidths and/or lengths to be used depending on the size, shape andlocation of the facet joint in which the resurfacing device is beinginserted.

The guide probe tip 204 may have a thickness and a width that are bothsmaller than a thickness and a width of the guide probe shaft 202. Incertain embodiments, the guide probe tip 104 has a width of betweenabout 5 millimeters and about 20 millimeters. In other embodiments, theguide probe tip 104 may have a width that is about 9 millimeters.

In certain embodiments, the guide probe tip 204 may have a thickness ofbetween about 0.10 millimeters and about 0.50 millimeters. In otherembodiments, the guide probe tip 204 may have a thickness of about 0.20millimeters.

The guide probe tip 204 may be formed with a proximal end that is notpointed. Forming the guide probe tip 204 with this configuration at theproximal end minimizes the potential that the guide probe tip 204 willdamage or other negatively impact the tissue in the facet joint orsurrounding the facet joint.

In certain embodiments, it is possible for the proximal end of the guideprobe tip 204 to be sharpened such that the guide probe tip 204 may beused to cut tissue when attempting to access the facet joint.

The guide probe tip 204 may be fabricated from a material that is rigidbut which is flexible. Forming the guide probe tip 204 from a flexiblematerial enhances the ability of the guide probe tip 204 to bepositioned at least partially in the facet joint as an initial step inimplanting the resurfacing body 46.

In certain embodiments, the guide probe tip 204 is fabricated from ametallic material such as stainless steel. It is also possible tofabricate the guide probe tip 204 from a non-metallic material using theconcepts of the invention.

An important criterion is selecting the material that is used tofabricate the guide probe tip 204 is that the material be biocompatible.If it is desired to reuse the guide probe tip 204 for multiple surgicalprocedures, the guide probe tip 204 should be capable of withstandingrepeated sterilization processes such as by using an autoclave.

The guide probe tip 204 may be attached to the guide probe shaft 202using at least one fastening device 212. In certain embodiment at leasttwo of the fastening devices 212 are used to attached the guide probetip 204 to the guide probe shaft 202.

The fastening device 212 may have a variety of different configurations.In one configuration, the fastening device 212 frictionally engages theguide probe shaft 202 through the aperture formed therein.Alternatively, the fastening device 212 may have a threaded side surfacethat enables the fastening device 212 to be screwed into the guide probeshaft 202 having an aperture with a complementary shape.

As an alternative to the configuration of the guide probe assembly 200configuration illustrated in FIGS. 10-12, alternative configurations ofthe guide probe assembly 200 may be utilized in conjunction with theconcepts of the invention. One such alternative configuration of theguide probe assembly is illustrated at 240 in FIG. 13. The guide probeassembly 240 includes an elongated main portion 242 and a handle portion244 that is attached to a proximal end of the main portion 242.

The main portion 242 may have a configuration that is similar to theguide probe shaft 202 illustrated in FIGS. 10-11. While FIG. 13illustrates that the main portion 242 does not have a separate tipportion, it is possible to adapt the concepts of this embodiments toencompass a separate tip portion so that the tip portion may possessdifferent physical characteristics that the main portion 242 from whichthe tip portion extends. Even when a separate tip portion is notprovided, a proximal end of the main portion 242 may be tapered tofacilitate guiding the guide probe assembly 240 to a desired location inthe facet joint.

The handle portion 244 enhances the ability to grasp the guide probeassembly 240 during the insertion process. In certain embodiments, thehandle portion 244 may have a width that is greater than a width of themain portion 242. The handle portion 244 may also have a thickness thatis greater than a thickness of the main portion 242.

The guide probe assembly 240 may be used in conjunction with the guideprobe assembly 200. In such a configuration, the main portion 242 may beplaced adjacent to the guide probe assembly 200. When used in thisconfiguration, the main portion 242 and the guide probe assembly 200 maybe thinner than with the separately used configuration so that the mainportion 242 and the guide probe assembly 200 may both fit inside of theguide cannula 260.

This configuration may utilize the handle portion 244 for guiding thedistal end of the guide probe assembly 200 into a position within thefacet joint. Thereafter, the guide probe assembly 240 may be withdrawn.Next, the guide cannula 260 may be placed over the guide probe assembly200.

The delivery system may include a guide cannula 260, as illustrated inFIGS. 14 and 15. The guide cannula 260 has an internal passage 262 thatextends from a proximal end to a distal end thereof. In certainembodiments, the passage 262 may have a generally rectangularconfiguration.

A width of the passage 262 is smaller than a width of the deliverycannula 280. In certain embodiments, the width of the passage 262 may bebetween about 3 millimeters and about 15 millimeters. In otherembodiments, the width of the passage 262 is between about 5 millimetersand about 10 millimeters.

A height of the passage 262 is smaller than a height of the deliverycannula 280. In certain embodiments, the height of the passage 262 maybe between about 0.50 millimeters and about 5 millimeters. In otherembodiments, the height of the passage 262 is about 2 millimeters.

To facilitate accurately positioning the guide cannula 260 with respectto the facet joint, the proximal end of the guide cannula 260 may have aconcave surface 266. The concave surface 266 may at least partiallyreceive a convex surface of the facet joint to thereby prevent the guidecannula 260 from moving laterally with respect to the facet joint andthereby enhance the ability to accurately insert the resurfacing deviceinto the facet joint.

The guide cannula 260 may include a first stop mechanism 270 proximate adistal end thereof. The first stop mechanism 270 limits a distance thedelivery cannula 280 may be inserted into the guide cannula 260. Incertain embodiments, the first stop mechanism 270 engages a stop surface286 that extends from an outer surface of the delivery cannula 280proximate a distal end thereof.

The guide cannula 260 may also include a second stop mechanism 272extending from the proximal end thereof. The second stop mechanism 272limits a distance the implant insertion tool 300 may be inserted intothe guide cannula 260 to thereby prevent over-insertion of theresurfacing device 46 into the facet joint. The second stop mechanism272 may engage a shoulder 320 on the implant insertion tool 310 when theimplant insertion tool 310 has been extended a desired distance into theguide cannula 260.

To enhance the ability to use the different components of the system,the second stop mechanism 272 may be positioned in a spaced-apartrelationship with respect to the first stop mechanism 270. In certainembodiments, a spacing between the first stop mechanism 270 and thesecond stop mechanism 272 is between about 1 centimeter and about 5centimeters.

The guide cannula 260 thereby facilitates extending the guide probeshaft 202 into the proximal end of the rectangular passage 262 until theproximal end of the guide cannula 260 is adjacent to the facet joint.Thereafter, the guide probe assembly 200 may be withdrawn from the guidecannula 260 by pulling the distal end of the guide probe assembly 200.

The guide cannula 260 may be fabricated with a length that enables thedistal end to be positioned proximate to the facet joint where theimplant is to be inserted while the proximal end is positioned outsideof the person's body. In certain embodiments, the guide cannula 260 mayhave a length of between about 10 centimeters and about 30 centimeters.

The delivery cannula 280 may have a generally rectangular profile with awidth and a height that are both slightly smaller than the width and theheight of the guide cannula 260. This configuration enables the deliverycannula 280 to be inserted into the guide cannula 260 after the guidestop assembly 200 has been removed from the guide cannula 260.

The delivery cannula 280 has an internal passage 282 that extends from aproximal end to a distal end thereof. In certain embodiments, thepassage 282 may have a generally rectangular configuration.

A width of the passage 282 is smaller than a width of the main portion312 of the implant insertion tool 310. In certain embodiments, the widthof the passage 282 may be between about 3 millimeters and about 15millimeters. In other embodiments, the width of the passage 282 isbetween about 5 millimeters and about 10 millimeters.

A height of the passage 282 is smaller than a height of the main portion312 of the implant insertion tool 310. In certain embodiments, theheight of the passage 282 may be between about 0.5 millimeters and about5 millimeters. In other embodiments, the height of the passage 282 isabout 2 millimeters.

Proximate the proximal end of the delivery cannula 280, the sides of thepassage 282 may be removed so that an upper face and a lower face of thedelivery cannula 280 define a pair of arms. When the implant insertiontool 310 is inserted into the delivery cannula 280, at least a part ofthe shoulder portion 320 may have a width that is greater than the widthof the delivery cannula 280, as illustrated in FIG. 24. Thisconfiguration thereby limits the distance that the implant insertiontool 310 may be inserted into the delivery cannula 280.

The delivery cannula 280 may include a pair of leaflets 284 that extendfrom a distal end thereof. The leaflets 284 may be fabricated from aresilient material. The leaflets 284 may be initially positionedadjacent each other.

The leaflets 284 may have a width that is approximately the same as awidth of the resurfacing body 46. A distal end of the leaflets 284 maybe curved. The curved distal end of the leaflets 284 thereby minimizesdamage to the superior articular face and the inferior articular face ofthe facet joint as the leaflets are moved into a position at leastpartially within the facet joint to provide an opening in the facetjoint that is adapted to receive the resurfacing body 46.

The leaflets 284 may deflect away from each other as the resurfacingbody 46 and the distal end of the implant insertion tool 310 extendtherebetween. The leaflets 284 thereby enable maintaining theresurfacing body 46 in engagement with the implant insertion tool 310.

The force required to separate the leaflets 284 should be sufficientlylarge so that the leaflets 284 are retained in the closed configuration.However, the force should not be too great such that it is difficult forthe resurfacing body 46 to be urged between the leaflets 284 during theimplantation process or that the leaflets 46 damage the resurfacing body46 when passing between the leaflets 284.

Proximate the proximal end of the delivery cannula 280, a stop mechanism286 may extend from at least one outer surface of the delivery cannula280. The stop mechanism 286 may be an elevated region that is orientedgenerally transverse to an axis of the delivery cannula 280.

In certain embodiments, the stop mechanism 286 may comprise two elevatedregions that are mounted in a spaced-apart configuration, as illustratedin FIG. 16. The two elevated regions thereby define a channel 288 thatextends therebetween. The channel 288 is adapted to receive a portion ofa leaflet retractor tool 360, which may be used to withdraw the deliverycannula 280 from the guide cannula 260.

The stop mechanism 286 engages the first stop mechanism 270 on the guidecannula 260. The stop mechanism 286 thereby limits a distance to whichthe delivery cannula 280 may be inserted into the guide cannula 260.

An embodiment of the invention may also include an implant insertiontool 310, as illustrated in FIG. 17. The implant insertion tool 310 mayinclude a main portion 312 and a handle portion 314 that is attached toa proximal end of the main portion 312.

The main portion 312 may have a width and a height that are slightlysmaller than the width and the height of the delivery cannula 280. Thisconfiguration enables the main portion 312 to be placed inside of andslide with respect to the delivery cannula 280 during the process ofinserting the resurfacing body 46.

In certain embodiments, the width of the main portion 312 may be betweenabout 3 millimeters and about 15 millimeters. In other embodiments, thewidth of the main portion 312 is between about 1 millimeter and about 5millimeters.

In certain embodiments, the height of the main portion 312 may bebetween about 0.5 millimeters and about 5 millimeters. In otherembodiments, the width of the main portion 312 is about 2 millimeters.

Proximate the intersection with the handle portion 314, the main portion312 may include a shoulder 320 extending from at least one side thereof.The shoulder 320 may be used to limit a distance to which the implantinsertion tool 310 may be inserted into the delivery cannula by engagingthe second stop mechanism 272 on the guide cannula 260.

The handle portion 314 may be oriented generally perpendicular to themain portion 312. The handle portion 314 thereby provides an enlargedsurface that may be used to grasp the implant insertion tool 310 andthereby facilitates manipulating the implant insertion tool 310. Incertain embodiments, the length of the handle portion 314 may be betweenabout 5 centimeters and about 15 centimeters.

A distal end 322 of the main portion 312 may include a concave surface323 that is curved to at least partially conform to a surface of theresurfacing body 46. The concave surface thereby enhances the ability toretain the resurfacing body 46 in a desired position with respect to theimplant insertion tool 310

To further enhance the ability to maintain the resurfacing body 46 in adesired location with respect to the implant insertion tool 310, anextension 324 may extend from the distal end 322. The extension 324 isadapted to engage the engagement feature 80 that is provided in theresurfacing body 46.

The extension 324 may have a shape that is similar to but slightlysmaller than the engagement feature 80. In particular, the extension 324may include a first extension region 326 a and a second extension region326 b.

The first extension region 326 a has a width that is smaller than thewidth of the first aperture region 81 a. The second extension region 326b has a width that is larger than the width of the first aperture region81 a and smaller than the width of the second aperture region 81 b. Thisconfiguration enables the extension 324 to be retained in the engagementfeature 80 to prevent the resurfacing body 46 from being separated fromthe implant insertion tool 310. More details on the relative size of theengagement feature 80 and the extension 324 are discussed above.

FIGS. 21 and 22 illustrate the relationship between the resurfacing body46 and the implant insertion tool 310. In FIG. 21, the resurfacing body46 is placed adjacent to but spaced-apart from the implant insertiontool 310. In FIG. 22, the resurfacing body 46 is in engagement with theimplant insertion tool 310 such that the extension 324 extends into andengages the engagement feature 80. The shape of the engagement feature80 may be approximately the same as the shape of the extension 324.

Since the accurate placement of the resurfacing body 46 within the facetjoint plays an important role in successfully treating the patient, theimplant insertion tool 310 is configured to be inserted into thedelivery cannula 280 and the guide cannula 260 until the handle portion314 engages the second stop mechanism 272 on the guide cannula 260. Thisconfiguration protects against inadvertent over insertion of theresurfacing body 46.

In certain situations depending on the shape of the facet joint wherethe resurfacing body 46 is being implanted, it may be desired to insertthe resurfacing body 46 to different distances in the facet joint. Tofacilitate accurately inserting the resurfacing body 46 to a desireddepth, embodiments of the invention utilize implant insertion tools 330and 340, as illustrated in FIGS. 18 and 19. These implant insertiontools 330, 340 provide for selected countersinking of the resurfacingbody 46 in the facet joint.

Other than the features set forth below, the implant insertion tools330, 340 have a similar configuration to the implant insertion tool 310illustrated in FIG. 17. The implant insertion tool 330 in FIG. 18includes a countersink extension 332 that extends from the distal endthereof. The countersink extension 332 may have a concave end surface334 that with a curvature that is similar to a curvature of theresurfacing body 46.

Similar to the embodiment in FIG. 17, an extension 336 is provided onthe countersink extension 332 that facilitates attachment of theresurfacing implant 46 to the implant insertion tool 330.

The end surface 334 is spaced apart from the concave surface 322. Incertain embodiments, the distance between the end surfaces may bebetween about 1 millimeter and about 10 millimeters. In otherembodiments, the distance between the end surfaces may be about 3millimeters.

The countersink extension 332 may have a width and a height that aresmaller than the width and the height of the main portion 312. Such aconfiguration minimizes the potential of contact between the countersinkextension 332 and the tissue within the facet joint, as such contactcould cause undesirable side effects.

The implant insertion tool 340 in FIG. 19 is similar to the implantinsertion tool 330 in FIG. 18 except that the countersink extension 342is slightly longer. In certain embodiments, the countersink extension342 may have a length of about 5 millimeters.

It is also possible to utilize a countersink positioner 350, asillustrated in FIG. 20 in conjunction with positioning the resurfacingbody 46 at a desired location within the facet joint. The countersinkpositioner 350 is similar to the implant insertion tool 330 illustratedin FIG. 18 except that the countersink positioned 350 does not includean extension extending from a distal end thereof.

The countersink positioner 350 may thereby be utilized after theresurfacing body 46 has been inserted into the facet joint when it isrecognized that the resurfacing body 46 is not inserted far enough intothe facet joint. After removing the implant insertion tool 310 from thedelivery cannula 280, the countersink positioner 350 is inserted intothe delivery cannula 280.

Similar to the handle portion 314 on the implant insertion tool 310limiting a distance that the implant insertion tool 310 may be insertedinto the delivery cannula 280, the handle portion 352 on the countersinkpositioner 350 limits the distance that the countersink positioner 350may be inserted into the delivery cannula 280 so that the resurfacingbody 46 may be accurately positioned within the facet joint.

In operation, an incision is made in the patient proximate to the facetjoint where it is desired to implant the resurfacing body 46. The guideprobe assembly 200 is inserted into the patient so that the guide probetip 204 can be used to identify the joint line in the facet joint.

Next, the guide cannula 260 is slid over the guide probe assembly 200,as illustrated in FIG. 28, until the distal end of the guide cannula 260is adjacent to the facet joint. The guide probe assembly 200 therebyenables the guide cannula 260 to be accurately and quickly placed in thelocation for the implanting process.

The guide probe assembly 200 is then withdrawn from the guide cannula260 with care being exercised to maintain the guide cannula 260 in astationary position with respect to the facet joint. Thereafter, thedelivery cannula 280 is inserted into the guide cannula 260 until a rib281 on the delivery cannula 280 engages the first stop mechanism 270, asillustrated in FIG. 23. The first stop mechanism 270 thereby limits thedistance to which the delivery cannula 280 may be inserted into theguide cannula 260.

In this configuration, the leaflets 284 extend from the distal end ofthe guide cannula 260. As the distal end of the guide cannula 260 isadjacent to the facet joint, the leaflets 284 extend into the facetjoint to cause a region to be formed where the resurfacing body 46 maybe inserted in subsequent operations.

Next, the resurfacing body 46 is positioned adjacent to the distal endof the implant insertion tool 310 so that the extension 324 extends intothe engagement feature 80, as illustrated in FIG. 22. The implantinsertion tool 310 is then inserted into the proximal end of thedelivery cannula 280.

When the implant insertion tool 310 is almost completely inserted intothe delivery cannula 280, the resurfacing body 46 is recessed in thedelivery cannula 280, as illustrated in FIG. 24.

In some embodiments, it may be desirable to use a leaflet spreader (notshown) that maintains the leaflets 284 in a spaced apart configurationsuch that the resurfacing body 46 may be positioned between the leaflets284. If it is desired to use the leaflet spreader, the loading processmay be changed slightly so that the resurfacing body 46 is attached tothe implant insertion tool 310 and then the implant insertion tool 310is inserted into the delivery cannula 280.

The insertion of the implant insertion tool 310 is continued until theresurfacing body 46 begins to extend from the distal end of the deliverycannula 280, as illustrated in FIG. 24. At this time, the shoulder 320engages the second stop mechanism 272 to limit the distance to which theimplant insertion tool 310 may be inserted into the delivery cannula280. As noted above, the leaflets 284 are deflectable to provide a spacefor the resurfacing body 46 to be inserted into the facet joint.

Next, the delivery cannula 280 is urged away from the facet joint, asillustrated in FIG. 26. This motion causes the leaflets 284 to berefracted to within the delivery cannula 280. The facet joint returns toits initial position, which causes the resurfacing body 46 to fill thespace between the bones.

In certain circumstances, it may be desirable to use a leaflet retractortool 360 such as is illustrated in FIG. 27 to cause the delivery cannula280 to be urged away from the facet joint. The leaflet refractor tool360 includes a first handle section 362 and a second handle section 364that are pivotally mounted with respect to each other.

The first handle section 362 engages the handle portion 314 on theimplant insertion tool 310. In certain embodiments, the handle portion314 may have an aperture that extends therethrough and the first handlesection 362 may be extended through the aperture to secure the leafletretractor tool 360 with respect to the implant insertion tool 310.

Thereafter, an end of the second handle section 364 engages a lip 366extending from the delivery cannula 280 proximate a proximal endthereof. The second handle section 364 is pivoted with respect to thefirst handle section 362 as indicated by arrow 368. This pivoting motioncauses the delivery cannula 280 to be urged away from the facet joint sothat the leaflets 284 are retracted to within the guide cannula 260.This motion is towards the facet joint to reduce the potential that theguide cannula 260 is moved from its desired position against the facetjoint during the implanting process.

Thereafter, the implant insertion tool 310 may be separated from theresurfacing body 46 using a gentle pull away from the resurfacing body46 to leave the resurfacing devices 42, 44 in the facet joint asillustrated in FIG. 29. The implantation process is thereby complete.Medical imaging may be used to evaluate whether the resurfacing body hasbeen accurately implanted prior to removing the guide cannula 260 fromadjacent to the facet joint.

In the preceding detailed description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the Figure(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thepreceding detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is contemplated that features disclosed in this application, as wellas those described in the above applications incorporated by reference,can be mixed and matched to suit particular circumstances. Various othermodifications and changes will be apparent to those of ordinary skill.

1. A method of treating a facet joint of a patient, wherein the facetjoint includes a superior articular face and an inferior articular face,wherein the method comprises: securing an implant to an implantinsertion tool by mating a first engagement feature on the implant witha second engagement feature on the implant insertion tool; positioning adistal end of a guide cannula proximate the facet joint, wherein theguide cannula has an internal passage extending therethrough; slidingthe implant through the guide cannula passage until the implant passesthrough a distal end of the guide cannula passage and is at leastpartially between the superior articular face and the inferior articularface; and exerting a force of at least 1 Newton on the implant insertiontool to separate the first engagement feature and the second engagementfeature.
 2. The method of claim 1, wherein the first engagement featurecomprises a first aperture region and a second aperture region, whereinthe first aperture region intersects an edge of the implant, wherein thesecond aperture region is in communication with the first apertureregion, wherein the second engagement feature comprises a firstextension region and a second extension region, wherein the secondextension region is attached to the implant insertion tool, wherein thefirst extension region is attached to the second extension regionopposite the implant insertion tool and wherein the first extensionregion is seated in the second aperture region when the implant issecured to the implant insertion tool.
 3. The method of claim 1, whereinsliding implant through the guide cannula passage comprises: sliding theimplant through an internal passage in a delivery cannula, wherein thedelivery cannula comprises a pair of leaflets mounted proximate a distalend thereof and wherein the leaflets are fabricated from a resilientmaterial; and sliding the delivery cannula through the guide cannulapassage.
 4. The method of claim 1, and further comprising: engaging theimplant insertion tool with a first handle section of a retractor tool;engaging the delivery cannula with a second handle section of theretractor tool; and pivoting the first handle section with respect tothe second handle section to cause the implant insertion tool to movewith respect to the delivery cannula.
 5. The method of claim 1, whereinthe implant comprises a first implant portion and a second implantportion.
 6. The method of claim 5, wherein the first implant portion andthe second implant portion each have a plurality of teeth formed on atleast one surface thereof.
 7. The method of claim 5, further comprising:positioning the first implant portion and the second implant portion ina stacked arrangement; loading the first implant portion and the secondimplant portion into an internal passage of a delivery cannula, whereinthe delivery cannula assembly has a distal end and defining the deliverycannula passage to be open at the distal end; slidably disposing animplant insertion tool into the delivery cannula passage, wherein adistal portion of the implant insertion tool abuts the first implantportion and the second implant; positioning the distal end of thedelivery cannula assembly to the facet joint; and sliding the implantinsertion tool distally within the delivery cannula passage to eject thefirst implant and the second implant from the distal end and at leastpartially between the superior articular face and the inferior articularface.
 8. The method of claim 5, wherein the first implant portion andthe second implant portion each comprise a first engagement feature andthe distal portion of the implant insertion tool has a second engagementfeature and wherein the first engagement feature is matable with thesecond engagement feature.
 9. The method of claim 1, wherein the implanthas a diameter of between about 5 millimeters and about 13 millimetersand a thickness of between about 0.25 millimeters and about 4millimeters.
 10. The method of claim 1, and further comprising defininga joint line in the facet joint by extending a guide probe assemblybetween the superior articular face and the inferior articular face,wherein the guide probe assembly has a width that is smaller than awidth of the guide cannula passage and wherein the guide probe assemblyhas a height that is smaller than a height of the guide cannula passage.11. A system for treating a facet joint of a patient, wherein the facetjoint includes a superior articular face and an inferior articular face,wherein the system comprises: an implant configured to selectivelyconform to a shape of at least one of a superior articular face of afacet joint and an inferior articular face of the facet joint, whereinthe implant comprises a first engagement feature; and an implantinsertion tool having a second engagement feature that is capable ofmating with the first engagement feature, wherein a force to separatethe first engagement feature and the second engagement feature aftermating is at least 1 Newton.
 12. The system of claim 11, wherein theforce to separate the first engagement feature and the second engagementfeature after mating is between about 1 Newton and about 10 Newtons. 13.The system of claim 11, wherein: the first engagement feature comprisesa first aperture region and a second aperture region, wherein the firstaperture region intersects an edge of the implant and wherein the secondaperture region is in communication with the first aperture region; andthe second engagement feature comprises a first extension region and asecond extension region, wherein the second extension region is attachedto the implant insertion tool and wherein the first extension region isattached to the second extension region opposite the implant insertiontool.
 14. The system of claim 13, wherein a width of the first apertureregion is smaller than a width of the second aperture region, wherein awidth of the first extension region is larger than a width of the secondextension region and wherein the width of the first aperture region islarger than the width of the first extension region.
 15. The system ofclaim 11, wherein the implant comprises a first implant portion and asecond implant portion, wherein the first engagement feature is formedin at least one of the first implant portion and the second implantportion.
 16. The system of claim 15, wherein: the first implant portionexhibits sufficient flexibility to transition from a relatively flatstate to an inserted state in which the first implant portionsubstantially matches any multi-planar curvatures of the superiorarticular face; and the second implant portion exhibits sufficientflexibility to transition from a relatively flat state to an insertedstate in which the second implant portion substantially matches anymulti-planar curvatures of the inferior articular face.
 17. The systemof claim 15, wherein the first implant portion and the second implantportion each comprise a first side and a second side, wherein the firstside has a plurality of teeth extending therefrom and wherein the secondside is substantially flat.
 18. The system of claim 17, wherein theplurality of teeth comprise a first set of teeth, a second set of teethand a third set of teeth, wherein the first set of teeth are orienteddifferently than the second set of teeth and the third set of teeth. 19.The system of claim 15, wherein the first implant portion and the secondimplant portion each define an anchoring surface and an articulatingsurface, wherein the system is configured such that upon insertion intoa facet joint, the articulating surfaces abut one another in a slidinginterface.
 20. The system of claim 15, wherein the first implant portionand the second implant portion each have a circular shape that isdefined by a diameter in the range of between about 5 and about 13millimeters.
 21. The system of claim 1, wherein the implant has athickness of between about 0.25 and about 4 millimeters, wherein theimplant insertion tool has a thickness that is approximately the same asa thickness of the implant and wherein the implant is formed ofpolyetherketone-based plastic.
 22. A kit for treating a facet joint of apatient, wherein the facet joint comprises a superior articular face andan inferior articular face, wherein the kit comprises: a superiorimplant configured to selectively transition to a shape that at leastpartially conforms to a shape of a superior articular face of a facetjoint; an inferior implant configured to selectively transition to ashape that at least partially conforms to a shape of an inferiorarticular face of the facet joint, wherein the superior implant isseparate from the inferior implant, wherein at least one of the superiorimplant and the inferior implant comprises a first engagement feature;and an insertion tooling set comprising: a delivery cannula having aninternal passage, a guide cannula having an internal passage; and animplant insertion tool sized to be slidably received within the deliverycannula passage, wherein the implant insertion tool comprises a secondengagement feature that is capable of mating with the first engagementfeature, wherein a force to separate the first engagement feature andthe second engagement feature after mating is at least 1 Newton; whereinthe kit is configured to provide an insertion arrangement in which thesuperior implant, the inferior implant and the implant insertion toolare slidably received within the delivery cannula passage, wherein thesuperior implant and the inferior implant are stacked against oneanother adjacent a distal region of the implant insertion tool.
 23. Thekit of claim 22, wherein the superior implant and the inferior implantare identical, wherein the superior implant and the inferior implanteach have a diameter of between about 5 millimeters and about 13millimeters and a thickness of between about 0.25 millimeters and about4 millimeters and wherein the superior implant and the inferior implantare each formed of a polyetherketone-based material.